The present invention relates to a filter device comprising a filter element arranged in a filter housing that can be sealed by a housing lid with a sealing ring, wherein a medium to be filtered is supplied to the filter element through an inlet opening in the filter housing, and filtered medium is discharged on the filtered side of the filter element through an outlet opening in the filter housing. The filter device of the present invention is particularly suitable for use as a crankcase ventilation filter.
Filter devices for crankcase ventilation, which are also referred to as oil separators, are used to filter and purify oil-containing air from the crankcase. The separated oil is returned to the oil circuit, and the cleaned air is normally introduced into the intake tract of the internal combustion engine. The filter device comprises a filter element in a filter housing, to which the oil-containing air is supplied through an inlet opening. The purified air is removed through an outlet opening in the filter housing. For safety reasons, a pressure relief valve is integrated into the housing lid. This pressure relief valve is under the pressure of the inlet side or the unfiltered side of the filter element, and when an overpressure limit is exceeded it moves to the open position to relieve the pressure in the filter housing.
Such filter devices are normally cylindrical in shape. The pressure relief valve is usually located in a housing lid that is placed on an axial end face of the filter housing. The pressure relief valve is fixed to the housing lid and is held in the closed position by a valve spring. As soon as the pressure in the filter housing exceeds a value that causes the pressure relief valve to open against the force of the valve spring, the oil-containing air flows through the valve out of the filter housing.
The housing lid is disposed on or in an axial housing opening on the end face of the filter housing and is sealed by a circumferential sealing ring located between the inside of the wall of the housing opening and the outside of the housing lid. The housing lid is normally screwed into the housing opening. For this purpose, a thread is provided between the wall of the housing opening and the housing lid.
When the housing lid has to be removed, e.g., for maintenance purposes, there is a risk that the rotational motion that is required to open the housing lid may damage the sealing ring. Especially if the sealing ring has remained installed for a prolonged period of time between the wall of the housing opening and the housing lid, it may be tightly stuck between the two components. As a result, a relative rotational motion between the filter housing and the housing lid can lead to strong forces acting on the sealing ring in circumferential direction, which can damage the sealing ring. The adhesion of the sealing ring also requires substantially more force to open the housing lid.